1. Field of the Invention
The present invention relates to a color reduction processing apparatus and color reduction method that converts image data containing multiple colors, including full-color image data, to image data containing fewer colors.
2. Description of the Related Art
Each pixel in a 24-bit depth full-color RGB image contains color data typically expressed as a combination of three primary colors (e.g., red (R), green (G), and blue (B)), each of which is defined by one of a possible 256 levels. To print this color data using a limited number of colors requires color reduction. Common basic color reduction methods include error diffusion, dithering, and halftoning. Achieving print results that are as close as possible to the original full-color image using just these methods is, however, difficult. One conventional method of solving this problem is to first reduce the full-color image to an 8-color image by dithering, and then further reduce this 8-color image to two or three colors using the luminance values of the 8-color image data to achieve print results that are closer to the original full-color image. See, for example, Japanese Unexamined Patent Appl. Pubs. 2002-269550, 2002-288682, and 2002-314833.
The foregoing prior art enables the processing of print data based on luminance values, for example, and thus enables such image processing effects as emphasizing contours and generating distinctive images emphasizing specific parts of the original image data. The problem is that the printed output (i.e., the printed image) can differ greatly from the original full-color image. A further problem is that the operation and process required for color reduction processing are complicated.